Note: Descriptions are shown in the official language in which they were submitted.
:~Z99~3~3
1 BACKGROUND OF THE INVENTION
The present invention relates to an
electromagnetic fuel injector and a method of producing
the same. More particularly, the invention is concerned
with an electromagnetic fuel injector suitable for use in
automotive engines, and also to a method of producing such
a fuel injector.
Japanese Patent Laid-Open Publication No.
119364/1985, particularly Fig. 1 of the drawings attached
thereto, shows a typical known electromagnetic fuel
injector.
The fuel injector has a movable valve part which
is integrally composed of a ball valve 11, a plunger rod
10 and a plunger 7 which serves as a movable core. In
operation, an electrlc current is supplied to a solenoid
coil 4 so that a magnetic circuit is formed so as to
include the plunger~7, a stator~core~2 and a yoke 6 so
that a magnetic attracting force is generated to enable
~;~ the stator core 2 to~attract the plunger 7. When the
supply of the electric current to the solenoid coil 4 is
ceased, the magnetic attracting force is extinguished so
that the movable valve part is reset to the origlnal
position by the force of the spring 5.~
Usually, the mechanical connection between the
stator 2 and ~he yoke 6 is attained by caulking by means
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1 of a jig which is moved downward onto the brim of an open-
ing in the yoke so as to plastically deform the ~aterial
of the yoke simultaneously over the entire circumference
of the opening in the yoke.
s This connecting method, however, is disadvan-
tageous in that the center of the caulking force applied
to the peripheral region of the connecting portion tends
to be deviated from the center of the opening in the yoke,
so that a difficulty is encountered in uniformly caulking
the yo~e. The yoke also tends to be deformed to cause an
offset between the axes of the yoke and the stator core in
the assembled state.
Furtnermore, since the precision of the const-
ruc~ion of a fuel injector depends on the radial size of
lS the stator core and the length of the surface at which the
stator core is coupled to the yokel the caulking method
mentioned above inherently has a possibility of a large
eccentricity, resulting in a large fluctuation of the
assembly preclsion in the axial direction which often
reaches 0.06 mm (see Fig. 4).
In the known fuel injector in which the yoke and
the stator are fixed to each other by caulking, it is
necessary that a valve guide and a plunger rod gulde have
large lengths in order to ensure a smooth and precise
reciprocating movement of the movable core. The use of
such long valve guide and long plunger rod guide inevit-
ably increases the size of the fuel injector and compli-
cates the construction of the same.
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SUMMARY OF THE INVENTION
. Accordingly, an object of the present invention is
to provide a fuel injector having a high assembly precision,
as well as a method of producing the same, thereby overcoming
the above-described problems of the prior art.
In accordance with one aspect of the invention there
is provided an electromagnetic fuel injector comprising: a
cylindrical yoke constituting a body of said fuel injector,
said yoke having an axial bore at an upper part therein and an
axially penetrating hole communicated with the bore in a
bottom part thereof, the hole having a diameter smaller than
that of the bore; a solenoid coil and a stator core received
in the axial bore of said cylindrical yoke, said stator core
having a flange portion; a movable core disposed in said
penetrating hole coaxially with said stator core and being
adapted to be attrac~ed by said stator core; and a movable
valve responsive to said movable core so as to be moved into
and out of contact with a fuel injection valve seat in
accordance with the balance of force between an
electromagnetic force produced by said solenoid coil and a
.~ force produced by a spring received in said stator core;
~- wherein an inner peripheral surface of said cylindrical yoke
defining the bore is formed to be substantially straight in an
axial direction thereof; said flange of said stator core is
fitted in the inner peripheral surface of said cylindrical
yoke, said flange having an engagement groove in an outer
peripheral surface portion thereof; and means precisely
positioning said stator core and said cylindrical yoke in
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coaxial relationship with respect to each other, said meansconsisting essentially of a coupling formed between said inner
peripheral surface of the yoke and the outer peripheral
surface portion of the flange of the stator core wherein a
part of the material of an edge portion of the inner
peripheral surface of said yoke which has been plastically
deformed locally is forced into thle engagement groove in the
outer peripheral surface portion of the flange of said stator
.: core by an elastic compressive stress therein, so that said
stator core and said yoke are coupled to and held on each
other.
In accordance with another aspect of the invention
there is provided a method of producing an electromagnetic
fuel injector comprising: disposing a cylindrical yoke having
a penetrating hole in a bottom part there of and a bore
communicated with the penetrating hole at a lower end thereof
and opened at an upper end thereof concentrically with respect
to a cylindrical center guide pin in such a manner that the
cylindrical center guide pin is fitted into the penetrating
. 20 hole of the cylindrical yoke to support the cylindrical yoke;
disposing, concentrically with respect to the cylindrical
. center guide pin, an outer guide around the cylindrical yoke
to support an outer periphery of an upper part of the
cylindrical yoke; disposing a stator core having a central
tube-like portion and a collar portion extended radially
outward from a middle part of the central tube-like portion,
with the outer periphery of the collar portion having a
coupling groove therein concentrically with respect to the
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cylindrical center guide pin in such a manner that a lower end
of the central tube like portion is supported by the
cylindrical center guide pin inserted therein, and the outer
periphery of the collar portion where the groove is formed is
contacted with a periphery of the.bore of the cylindrical
yoke; and pressing locally an inner peripheral edge of an
upper end of the cylindrical yoke vertically downwardly, while
keeping concentricities of the stator core, the cylindrical
- yoke, the cylindrical center guide pin, and the outer guide,
lo to plastically flow material of the cylindrical yoke into the
coupling groove of the collar thereby fixing the cylindrical
yoke with the stator core.
The above and other objects, features and advantages
of the present invention will become clear from the following
description of the preferred embodiment when the same is read
in conjunction with the accompanying
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lZ990~
1 drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a longitudinal sectional view of a
fuel injector embodying the present invention;
Fig. 2 is a longitud:inal sectional view of an
essential portion of the fuel injector shown in Fig. 1,
illustrating particularly the manner in which a stator
core is fixed to a yoke;
Fig. 3 is a graph illustrating the fluctuation
in the assembly precision in the assembly of the fuel
injector of the present invention in comparison with that
in the fuel injector; and
Fig. 4 iS a graph illustrating the precision
assembly of the fuel in~ector in accordance with the
present invention and that of a prior art fuel injector.
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DESCRIPTION OF THE PREPERRED EMBODIMENTS
Referring to~Fig. 1, a stator core 1 has a
central bore constituting a fuel passage la. The stator
core 1 also has a collar lb formed on the outer peripheral
surface at an axially intermediate portion thereof. An
annular coupling groove lc is formed in an upper portion
of the outer peripheral~surace of the collar lb.
As will be understood fro~ this Figure, the
coupling groove lc has an uneven cross-section having a
substantially W-like shape. A cylindrical yoke 2 has a
portion surrounding~the stator core lo A part of the
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~LZ~9038
1 inner peripheral portion of the cylindrica~ yoke 2 has
been plastically deformed to fill the coupling groove so
as to couple the cylindrical yoke 2 onto the stator core
1. An insulating bobbin 13, having a resin-molded annular
exciting coil 14, fits in the space between the outer
peripheral surface of the stator core I and the inner
peripheral surface of the yoke 2, through the inter-
mediates of "0" rings l and 2
The stator core 1 has a central bore 1 which
receives a cylindrical adjusting sleeve 12 which is fixed
therein by caulking effected from the outer side of the
stator core 1. A ball valve 3 disposed on the lower end
of the stator core 1 is held on the lower end of a
cylindrical plunger rod 4 which in turn is press-fit to
the inner side of a cylindrical plunger 5 which opposes
the stator core l leaving a predetermined axial gap
therebetween. A guide ring~6 made of a~non-magnetic
material and having one end connected by, for example,
press-fit in the plunger 5 while the other end is slidably
received in the bore of the stator core 1. A spring 11 is
disposed in the guide ring 6 with its both axial ends
acting on the plunger rod 4 and the adjusting sleeve 12 so
as to normally~bias the ball valve 3 in the closing
direction.
The fuel injector further has a nozzle 7 having
a nozzle port 7a. The nozzle 7 is disposed coaxlally with
the valve guide 9 and; Iz fixed to the latter as the
material of the o~te~r peripheral portion thereof is
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1 locally and plastically deformed to fill an annular groove
9a formed in the inner peripheral surface of the valve
guide 9.
The valve guide 9 is disposed in a cylindrical
recess 2a formed in the lower end surface of the yoke 2,
through the intermediary of a C-shaped washer 10.
The fixing of the valve guide 9 to the yoke 2 is
attained by causing a portion of the yoke 2 to be plasti-
cally deformed into an annular groove 9a formed in the
outer peripheral surface of the valve guide 9 so as to
fill this annular groove 9a.
The stator core 1 and the yoke 2 are capped with
a plastic jacket 15A~molded from a plastlc. The plastic
jacket 15 is provided at its one end with a terminal plug
15a through which lead wires are extended and a rubber
bush 15B is seated on the plastic jacket 15A.
A reference numeral 15C~denotes a metallic
filler disposed in the fuel passage.
The~fuel injector of the invention having the
described construction is assembled;by a method which will
be described hereinunder.
Referring to Fig. 2, the yoke 2 is immovably set
on a center guide 17 which is sized to fit in the bore of
the yoke 2 so as to guide the yoke 2. At the same time,
the yoke 2 is held at its outer peripheral surface by an
outer guide 18~which is fixed to a lower die 21.
Subsequently, the solenoid coil 14 is placed on and around
the guide 17 together with the insulating bobbin 13.
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1 The stator core 1 is then brought into axial
alignrnent with the yoke 2 and is slided along the guide 17
so as to be set in the yoke 2 coaxially therewith.
Subsequently, a punch 16, which is set on a
press ram 22 through a fixing plate 20, is lowered while
being guided by the inner peripheral surface o~ the yoke
2. In consequence, an annular processing tooth on the
lower end of the punch 16 locally and vertically presses
the inner peripheral edge portion of the axial end surface
of the yoke 2 near the coupling portion. The pressing
force causes a portion of the materiaI of the yoke 2 to
plastically flow in a direction substantially perpendi-
cular to the pressing direction into a coupling groove
formed in the outer peripheral surface of the stator core
1, thereby coupling the stator core 1 and the yoke 2 to
each other. After the coupling, the press cam 22 andJ
hence, the punch 16 are raised and a knock-out pins 23 are
activated to eject the assembled part.
Subsequently, the adjusting sleeve 12 is fixed
in the thus assembled part, and the plunger rod 4 which
has been separately assembled is inserted through the
~; spring 11 and the C-shaped washer 10. Then, the valve
guide 9 having~the ball valve 3 set i~n the center thereof
and provided with the nozzle 7 fixed thereto is placed in
the bore of the yoke 2, and the inner peripheral edge
portion of the yoke 2 is locally and vertically pressed in
the same manner as that explained above, so that a portion
of the material of the yoke 2 plastically flows in a
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~Z9903~
1 direction substantially perpendicular to the pressing
direction into a coupling groove 9a formed in the outer
peripheral surface of the valve guide 9, whereby the valve
guide 9 is coupled to the yoke 2.
In the described method of the invention, the
coupling between the yoke 2 and the stator core 1 is
conducted while the yoke 2 and the stator core 1 are
coaxially guided at their inner peripheral surfaces by a
common guide 17. Namely, the stator core 1 is located by
the guiding peripheral surface 17A of the guide 17 while
the yoke 2 is located by the guiding peripheral surace
17B of the guide 17 so that the yoke 2 and the stator core
1 are precisely held coaxially with each other during the
; coupling operation, thus assuring a high degree of axial
. 15 alignment between the yoke 2 and the stator core i. In
addition, the coupling portion is not subjected to any
large external cau1king force but is merely locally
: deformed plastically so that a high degree o~ dimensional
precision is maintained in the connection between the yoke
2 and the stator core l. Furthermore, the coupling by the
local plastic deformation can easily be effected by a ~ :
simple yress, so that the method of the described embodi-:
~ ment can suitably be employed in mass-production.
:: The coupling of the valve guide also is effected
by a local plastic deformation caused by an axial pressing
force, so that the high precision of the coupling is
attained between the valve guide and the yoke, without
causing any degradation in the preclsion of the coupling
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1 between the yoke 2 and the stator core 1 attained by the
above-mentioned plastic deformation.
Fig. 3 shows the amount of fluctuation in the
assembly precision, particularly the amount of offset
between the axes of the yoke 2 and the stator core 1, as
observed in a fuel injector assembled by the method of the
invention and in a known fuel injector which has been
assembled by caulking. From this Figure, it will be seen
that the amount of offset in the fuel injector of the
present invention is as small as 1/3 that in the known
fuel injector.
Fig. 4 shows the degree of assembly precision in
terms of fluctuation in the axial gap a between the yoke 2
and the stator core 1. It will be seen that the fuel
injector the invention is superior to the known fuel
injector also in the assembly precision in terms of the
axial gap.
From Figs. 3 and 4, it will be understood that
the present invention ensures a higher~reliability of the
fuel injector as the~product, and off~ers a higher
efficiency in the mass-production of the fuel injector.
It i8 also to be understood that, in the fuel
injector of the invention, a high degree of axial
alignment between the yoke 2 and the stator core 1 is
attained and, in addition, the reciprocating movement of
the movable part including the ball valve 3, plunger rod 4
and the plunger 5 is smoothed by virtue of the ring 6
fixed to the plunger 5 so as to slide along the inner
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1 peripheral surface oE the stator core 1. This in turn
eliminates the necessity for large lengths of the valve
guide and the plunger rod which are essentially required
in the known fuel injectors. In consequence, the present
invention also offers a compact design of the fuel
injector.
In consequence, the present invention enables
the stator core and the yoke to be assembled together with
a high degree of easiness and reliability, thereby to
ensure a highly reliable and precise construction of the
fuel injector.
